The invention relates to a severing apparatus for sheet-laminating machines for separating sheets, transported as single sheets and coated with a continuous film layer, with severing of the overhanging film layer in the edge region of the overlapping area by means of a moving knife.
For sheet-laminating machines with the known single-sheet transport, it is necessary to sever the coated, continuous film layer at least partially in the overlapping area of the sheets before the sheets are decollated, in order to ensure that the film layer tears off along the desired tear line during the mechanical decollating process and that the film layer applied suffers no damage.
In order to bring this about, various severing apparatuses have already become known, which make use of different techniques, such as the installations described in the German patent application P 40 27 431.4-26 and the utility patent G 88 05 650.3.
The technique, described in the patent application P 40 27 431.4-26, makes use of two rolls, which are disposed opposite one another without contacting each other and between which the film-coated sheets run. The lower of the two rolls serves as counter-pressure roll, while the upper is equipped with knives or a plurality of points, depending on the embodiment.
If several perforating knives, disposed one behind the other, are used, the problem arises that, aside from the fact that the surface of the film layer is constantly in contact with the tearing roll for the purpose of driving the latter, the peripheral speed of the roll must be coordinated very accurately with the conveying speed of the sheets, in order to ensure that the knives dip precisely at the overlapping area into the film layer. Any adaptation to different sheet sizes is therefore very expensive. If a plurality of revolving points are used instead of the knives, the film surface is not in contact with the tearing roll, since the latter is mounted at a defined distance above the film layer and there is contact only in the double-layer overlapping area, which leads to the driving of the tearing roll. The expensive and difficult coordination of the peripheral speed of the roll with the conveying speed of the sheet can therefore be omitted. However, a larger area of the film surface, namely the whole of the overlapping area, is gripped by the points and perforated and thus damaged. Moreover, in contrast with an incised film layer, problems can arise with tearing and tearing off the perforated film layer.
The installation described in the utility patent G 88 05 650.3 has knives in motion, movably mounted on a carrier and moved by means of pneumatically controlled cylinders addressed by a control unit for severing the film layer. Continuous film layers, running in parallel as well as consecutively, can be incised with this arrangement. However, the control of the cylinders is very complicated and expensive. The same is true for the cutting units, which must be shifted manually on the carrier.
Admittedly, the German patent application P 42 32 332.0 describes a severing apparatus, the construction of which is simpler and which is easier to control than that of the aforementioned utility patent. Said severing apparatus also has a translatorily movable knife, which in this case can be attached to a pivotably mounted rocker arm moved by a stepping motor. However, both arrangements with translatorily moved knives have the disadvantage that, on the one hand, the knife must constantly slide on the sheet and can thus damage the sheet and that, moreover, a control is necessarily required, which detects the overlapping area, in order to control the motion of the knives, so that a cutting motion is initiated when such an overlapping section is traversed.